The invention relates to an indexable turning insert comprising two opposing large sides formed by a support centre part and a plurality of cutting parts projecting outwardly therefrom, each having a cutting edge extending between the sides and being spaced apart around the outer perimeter of the centre part for indexing, as well as a cutting tool comprising an indexable turning insert and an insert holder.
The invention is generally directed to turning inserts for carrying out any type of turning machining upon a rotating work piece, and it is particularly directed to such turning inserts for non-longitudinal turning, such as parting-off, grooving and transverse turning.
When using such a turning insert one cutting edge thereof is utilized for the turning operation until it is worn out or otherwise fails, such as is broken, whereupon the insert is moved, and put in a new position in an insert holder, i.e. indexed, for utilizing another of the cutting edges of the insert.
It is from the cost point of view desired to have, as many cutting parts and by that cutting edges as possible on such a turning insert, but an increased number of such cutting edges results at the same time in a reduced maximum depth of grooves when using the turning insert for grooving.
WO 03/070403 A1 discloses an indexable turning insert of the type defined in the introduction, which has 5 cutting edges making it comparatively attractive from the cost point of view, but it may only be used for obtaining comparatively shallow grooves when grooving and not be used for transverse turning, since the support centre part will then hit the work piece.
No known indexable turning insert of the type defined in the introduction being able to be used for transverse turning has more than 3 cutting edges making these inserts less attractive from the cost point of view.
It is desirable to provide an indexable turning insert of the type defined in the introduction being improved in at least some aspect with respect to such turning inserts discussed above.
According to an aspect of the invention, such an indexable turning insert which is further wherein:
it comprises four the cutting parts,
each cutting part has a clearance side extending on one of the sides of the insert from the cutting edge of the cutting part towards the centre part while making clearance angles in two dimensions with respect to the cutting edge,
the cutting edge of each cutting part makes a working lead angle being below 90° by less than the clearance angles with the other of the sides of the insert, and
every second of the cutting parts as seen in the direction of the outer perimeter of the insert have the clearance side on a same first side of the sides of the insert and the other two cutting parts have their clearance side on a second side of the sides of the insert for forming couples of mutually indexable cutting parts.
By combining the extension of each cutting edge with the clearance side and clearance angles of the cutting part in this way transverse turning may be carried out on a work piece having any dimensions in spite of the fact that the turning insert has four cutting edges making it more attractive from the cost point of view than known indexable turning inserts for such transverse turning. The turning insert according to the invention may also be designed to obtain a substantial depth when carrying out parting-off and grooving operations.
According to an embodiment of the invention the clearance angles of each cutting part are 2°-8°, 3°-6°, 3.5°-4.5° or substantially 4°. It has turned out that such clearance angles in two dimensions of the cutting parts of a turning insert according to the invention are suitable for combining with the angle made by the respective cutting edge for reliably obtain the behaviour of the insert aimed at while giving the cutting parts with cutting edges the longest possible life time.
According to another embodiment of the invention the angle made by the cutting edge of each cutting part with the other of the sides of the insert is below 90° by 1°-5°, 1.5°-3° or substantially 2°. These are suitable such angles for the extension of each cutting edge.
According to another embodiment of the invention the angle made by the cutting edge of each cutting part with the other of the sides of the insert is below 90° by a value of 40%-60% preferably substantially 50% of the clearance angles. This makes it possible to efficiently utilize the magnitude of the angles for the clearance side and the cutting edge for obtaining reliable operation of the insert over a long life time of each cutting edge.
According to another embodiment of the invention the insert has for each the large side the support centre part and the two cutting parts having the clearance side on the other large side extending in the same plane, and these planes for the two large sides extend in parallel with each other. This design of the insert with the cutting parts extending in the same plane as a support centre part on each large side of the insert on one hand facilitates the achievement of the proper operation of the insert when used for transverse turning, and on the other makes it possible to use the compression-moulding technique for manufacturing the insert, which is substantially less costly than injection moulding used for known turning inserts of corresponding type.
According to another embodiment of the invention the cutting parts are spaced apart for obtaining an indexing by rotating the insert substantially 180° about an axis being perpendicular to the opposing large sides. Thus, such indexing makes it possible to utilize two of the cutting edges, and the other two cutting edges may be used by turning the insert for mutually changing the direction of the two large sides thereof or moving the insert to another side of an insert holder of a cutting tool then changing possible transverse turning from left to right or conversely.
According to another embodiment of the invention the insert has one first lateral recess separating two adjacent cutting parts for forming lateral support surfaces of the insert facing away from a centre of the insert, and the insert has two the first lateral recesses, one between every second cutting part as seen in the direction of the outer perimeter. Such a recess may efficiently co-operate with a support wall having a complementary extension in a holder for the insert for firmly and by that reliably hold the insert in exact position during turning operation.
According to another embodiment of the invention the insert has at least one lateral support surface facing away from the centre of the insert between adjacent the cutting parts having no the first lateral recess therebetween, which then makes it possible to keep the insert properly in position in an insert holder by acting thereupon also in the direction towards this lateral support surface, such as by applying a pressure thereupon jamming the insert in place.
According to another embodiment of the invention the insert has an appearance with a butterfly-like character as seen in directions perpendicularly to the large sides, and each cutting edge may then form a wing tip of the butterfly. This type of appearance of the insert will make it easy to handle by reliably put it in proper positions and holding it in these positions.
According to another embodiment of the invention two adjacent of the cutting edges are pointing in substantially the same direction being substantially opposite to the direction in which the other two cutting edges point, which may also facilitate the handling of the insert.
According to another embodiment of the invention the extension of the clearance side of each cutting part from the cutting edge thereof towards the centre part is more than 5 mm, more than 6 mm or 7-12 mm. A turning insert with the features according to the invention may in spite of the existence of four cutting edges in this way be given parting-off depths of these values when carrying out parting-off or grooving.
The invention also relates, according to an aspect thereof, to a cutting tool comprising an indexable turning insert and an insert holder in which the insert holder is configured to hold the insert while keeping one the cutting edge to be presently used for cutting in parallel with an axis of rotation of a work piece to be machined. This means that the cutting tool may be used for transverse turning to the centre of a work piece in spite of the dimensions thereof and also for efficient parting-off and grooving.
According to an embodiment of the invention the insert holder comprises a body with a second recess having a bottom configured to form a support surface for one of the large sides of the insert, and this bottom is inclined with respect to outer surfaces of the body by an angle corresponding to the magnitude by which the angle of the cutting edge made with the other of the sides of the insert is below 90°. This makes it possible to firmly hold the insert in proper place and to use the insert, holder for such inserts having different thicknesses, i.e. different dimensions of their cutting edges.
According to another embodiment of the invention the insert holder comprises a body having a second recess for receiving the insert and a member configured to apply a pressure to the insert for keeping it in the second recess, and the member is then preferably configured to apply pressure on a lateral support surface of the insert for efficiently holding the insert by the holder.
According to another embodiment of the invention the tool comprises an insert, and the second recess in the body has a lateral support wall having an extension being complementary to the first lateral recess of the insert for supporting the insert received in the second recess of the holder.
According to another embodiment of the invention the second recess has a wall configured to form a support for lateral support surfaces of a the insert located opposite to the lateral support surfaces upon which the member is configured to apply a pressure, so that the insert may be efficiently jammed between the wall thereof and the member.
According to another embodiment of the invention the second recess is provided with a lateral aperture configured to accommodate the cutting edge of the insert located, oppositely to the one to be presently used for cutting, so that this cutting edge not used may be protected and not harmed when not in use.
According to another embodiment of the invention the insert holder is configured to hold a the insert received in a second recess thereof with only substantially the cutting part with the cutting edge to be presently used for cutting projecting with a clearance region thereof freely from the holder. Thus, the parts of the insert participating in supporting and holding the insert in the holder are completely independent of the cutting parts with cutting edge and clearance side thereof, so that the insert may be properly arranged in the holder for carrying out a turning operation with a cutting edge even if the cutting part of another cutting edge has been broken.
According to another embodiment of the invention the insert holder comprises a body provided with second recesses for receiving a the insert therein on opposite sides of the body and for holding the insert inclined in opposite directions by an angle being of a magnitude corresponding to how much the angle of the cutting edge made with the other of the sides of the insert is below 90° with respect to the respective side of two mutually parallel sides of the body. This means that the tool may be used for both left and right transverse turning without changing the position of the holder but only moving the insert from one second recess to the other.
The invention also relates to a use of an insert according to the invention for a tool according to the invention for parting-off and/or grooving and/or transverse, turning of a work piece as well as a method for manufacturing a turning insert according to the invention, which includes a step of compression-moulding material to the shape of the insert'.
Further advantages as well as advantageous features of the invention appear from the following description.